This invention relates to the separation of acid gases from gaseous mixtures. More particularly, this invention relates to the separation of acid gases, particularly CO.sub.2, from gas mixtures, the separation being characterized by the use of a selective absorbent.
A number of methods have been proposed previously for the purification of mixtures of industrial gases, such as hydrocarbon gases contaminated with hydrogen sulfide, carbonyl sulfide, carbon dioxide, and the like. Some of these methods involve the formation of salts of the acid gases, the salts being subsequently decomposed, usually by heating, to regenerate the solution utilized as an absorbent and to drive off the gas absorbed.
In many cases, aqueous solutions of alkanolamines and like materials are utilized. Such solutions have relatively limited solubility for CO.sub.2. This factor requires the recycling and treating of unduly large quantities of such solutions, as well as resulting in the utilization of unduly large amounts of heat to regenerate such solutions. Additionally, one of the most important disadvantages of the use of such solutions is the limited solubility for the acid gases when the latter are under a high partial pressure. Accordingly, only fractional removal of the acid gas from its admixture with hydrocarbons or other gaseous materials is obtained.
Contrasted to the use of so-called "chemical solvents" (involving the formation of salts or other decomposable reaction products), certain classes of materials are regarded as "physical solvents". These latter materials appear to act in a purely physical manner, absorbing acidic gases physically without the formation of any apparent reaction product. For example, mixtures of glycols with amines are known, particularly for the treatment of liquid hydrocarbon products for the removal of mercaptans, H.sub.2 S and other acidic substances. However, glycols have not been found to be very efficient due to the limited solubility of the acid gases therein. Aqueous dispersions of glycols are no better in this respect, and may exhibit extreme corrosiveness toward processing equipment.